Mitutoyo Correct Usage Series

Proper Use of Bore Gages

Bore gages are precision instruments used to accurately measure internal diameters by comparing them against a master reference. Commonly used both on the shop floor and in inspection rooms, bore gages provide reliable results—when used correctly.

Because they are comparative tools, improper preparation or technique can lead to subtle measurement errors that may go unnoticed.

Watch the video below to learn how Mitutoyo recommends using a bore gage to ensure accurate and consistent results.

Preparation Before Measurement: Key Points

• Check the operation of all parts and clean the bore gage thoroughly before use.

• Insert the bore gage into the setting ring, then mount the indicator until the needle is near the center of its measuring range.

• Sweep the gage back and forth to find the point where the highest value is displayed—this is your zero point.

• Rotate the bezel to align zero on the dial face with the indicator needle.

• If needed, rotate the bezel further to offset the reading to match the value of the setting ring.

• Always read the dial gage straight on to avoid parallax error.

Preparation Before Measurement: Video

Handling: Key Points

• Hold the grip securely to maintain stability while measuring.  

• Insert the bore gage at a slight angle from the contact point side, and remove it at an angle from the anvil side.  

• Always take the reading from the position where the dial indicator shows the maximum value.  

• To avoid parallax error, be sure to read the dial indicator directly from the front.

Handling: Video

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CG-AX Series - Standard Bore Gage

Mitutoyo offers a comprehensive range of bore gages equipped with interchangeable anvils and accessories for precise ID measurements, featuring durable carbide-tipped contact points, a rugged protective cover for the dial indicator, and optional extension rods for deep hole measurement.